A so-called buoyant antenna is disclosed in the paper “A Slender Resonator—Slot Antenna” by J. C. Lee, IEE International Conference on Antennas and Propagation, Conf. Publ. No. 195, pp 442–446, 1981. Essentially the antenna disclosed comprises a slot formed by the edge opening in a roll-resonator of copper clad plastic dielectric, approximately ½ free-space wavelength long. The slot is short circuited at the two ends, and the antenna is fed by a coaxial line the inner and outer conductors of which are soldered to respective sides of the slot. A modified antenna is disclosed in “UHF Buoyant Antenna” by M. S. Smith et al, IEE ICAP 87, pp 1.273–1.276, 1987. The modified antenna augments the “per unit length” capacitance by discrete capacitors connected across the slot, the length of the antenna being approximately equal to λ/2, where λ is the free space wavelength at the operating frequency of the antenna. The practical design disclosed in FIG. 1(b) of the paper comprises a cylindrical tube of metallic material on a dielectric former having a longitudinal slot which is shorted at each end and coupled to a coaxial feed at its center, the slot being bridged by two capacitances respectively positioned approximately midway between the center feed and the shorted ends. The antenna length is approximately λ/2 and operates in a weakly evanescent mode. However, there are applications in which a buoyant antenna is required which is limited to smaller dimensions imposed by physical constraints in its operating environment.